According to recent UBC research, whales brains have special blood vessels that may shield them from swimming-related blood pulses that could harm the brain.
There are numerous hypotheses regarding the precise function of the “retia mirabilia,” or “wonderful net,” networks of blood vessels that surround the brain and spine of a whale. However, UBC zoologists now think they have the answer, and computer modeling supports their claims.
When galloping, land mammals like horses experience “pulses” in their blood, where blood pressures inside the body rise and fall with each stride. In a new study, lead author Dr. Margo Lillie and her team make the first suggestion that whales, which swim with dorso-ventral movements, also experience the same phenomenon. And they may have discovered why whales avoid long-term brain damage for this reason.
The average blood pressure in arteries, or the blood leaving the heart, is higher than in veins in all mammals. According to Dr. Lillie, a research associate emerita in the UBC department of zoology, this difference in pressure controls blood flow throughout the body, including through the brain. However, moving around can jar the blood, sending “pulses” of pressure to the brain. The difference in pressure between when blood goes into and out of the brain during these pulses could cause damage.
According to Dr. Lillie, long-term damage of this nature can cause dementia in people. Whales hold their breath when diving and swimming, in contrast to horses, who regulate their breathing by inhaling and exhaling. Dr. Lillie explains that if cetaceans can’t use their respiratory system to control pressure pulses, they must have found another solution.
According to Dr. Lillie and colleagues, the retia use a “pulse-transfer” mechanism to make sure that, in addition to the average difference, there is no difference in blood pressure in the cetacean’s brain during movement. In essence, the retia transfers the blood’s pulses from the arterial blood entering the brain to the venous blood exiting, maintaining the same “amplitude” or strength of pulse, thereby preventing any difference in pressure within the brain itself.
One of the biomechanical parameters that the researchers took from 11 different species of cetaceans and put into a computer model was how often the animals fluked.
“Our model supports our prediction that locomotion-generated pressure pulses can be synchronized by a pulse transfer mechanism that reduces the pulsatility of resulting flow by up to 97 percent,” says senior author Dr. Robert Shadwick, professor emeritus in the UBC department of zoology. “Our hypothesis that swimming generates internal pressure pulses is new.”
According to Dr. Shadwick, the model may be used to answer questions about how other animals, including humans, move and what happens to their blood pressure pulses. Even though the researchers say that the hypothesis still needs to be directly tested by looking at the blood flow and pressure in the brains of swimming cetaceans, doing so would be unethical and technically impossible right now because it would require putting a probe inside a living whale.
As fascinating as they are, he claims that they are essentially inaccessible. They are the largest animals on the planet, if not ever, and it’s fascinating to learn how they manage to live and do what they do, according to basic biology.
The next step, according to co-author Dr. Wayne Vogl, professor in the UBC department of cellular and physiological sciences, would be to understand how the thorax reacts to water pressures at depth and how the lungs affect vascular pressures. Of course, direct measurements of blood flow and pressure in the brain would be extremely useful but are currently not technically feasible.
